How much caffeine is in Black tea?

A standard 240 ml (8.1 fl oz) cup of black tea contains 47 mg of caffeine, which equals 19.6 mg per 100 ml. This amount accounts for 12% of the FDA’s 400 mg daily limit for healthy adults and provides roughly half the caffeine of an equal-sized serving of drip coffee (96 mg per 240 ml).

That 47 mg falls squarely in the middle of the tea caffeine spectrum — lower than a bold English Breakfast brew (50 mg) or a spiced chai latte (50 mg), yet substantially more than a delicate white tea (16 mg), a classic green tea (28 mg), or a lightly oxidised oolong (37 mg). In terms of comparable everyday drinks, one cup of black tea has slightly more caffeine than a 355 ml can of Coca-Cola Zero (34 mg) and a little over half of a standard 250 ml Red Bull (80 mg).

For most healthy adults, the caffeine in black tea is absorbed within 15 to 45 minutes and can sustain a clear-headed energy for three to five hours. Unlike the rapid spike-jolt-crash pattern often associated with high-caffeine beverages, black tea’s moderate dose combined with its natural L-theanine tends to produce a smoother, more gradual rise in alertness and a gentle decline, making it a popular choice for sustained focus during work or study.

How long Black tea stays in your system

Caffeine follows first-order pharmacokinetics: the body eliminates a constant fraction per hour, not a fixed milligram amount. Using the population-average half-life of 5.7 hours, the 47 mg from one cup of black tea decays as follows: after 3 hours roughly 33 mg remain, after 6 hours 23 mg, after 9 hours 16 mg, and after 12 hours 11 mg. The decay formula is remaining = 47 × 0.5^(hours/5.7); for instance, at 3 hours: 47 × 0.5^(3/5.7) ≈ 32.6 mg, rounded to 33 mg.

If you finish your cup at 15:00 (3 p.m.), you will still have about 23 mg of caffeine circulating at 21:00 — roughly the amount in a small square of dark chocolate. By 23:00, that residual drops to roughly 18 mg (at 8 hours, 47 × 0.5^(8/5.7) ≈ 17.8 mg). For most people, this low level is unlikely to block sleep onset, but individuals who are slow metabolisers or highly sensitive may experience lighter or more fragmented sleep if the last cup is consumed within 6 hours of bed. Our latest cup before bedtime tool can personalise this window.

When you drink multiple cups, the caffeine stacks. If you start with 47 mg and add a second cup two hours later, the combined caffeine is roughly 47 + (47 × 0.5^(2/5.7)) ≈ 47 + 38 = 85 mg — nearly the level of a full-strength coffee. This means that spacing black tea throughout the day can build a cumulative effect that outlasts a single serving, so a person who drinks tea from morning to late afternoon could have over 100 mg still active at dinner time. Using the caffeine half-life calculator lets you test any scenario.

A single 47 mg cup of black tea is a lightweight contribution to the FDA and EFSA daily maximum of 400 mg for healthy adults: you could drink about 8.5 such cups before reaching the limit. However, total daily intake is not just about the ceiling; it is about how caffeine accumulates and clears. Because the half-life is 5.7 hours, drinking more than one cup every few hours builds a rising baseline. For example, three cups taken at 08:00, 11:00, and 14:00 can leave over 80 mg in your system by 20:00. Pregnant and breastfeeding individuals are advised by EFSA to stay at or below 200 mg per day, making about 4 cups of black tea the maximum from all caffeine sources combined.

When considering sleep, a widely cited study by Drake et al. (2013) found that 400 mg of caffeine taken 6 hours before bedtime still reduced total sleep by over an hour. For the much smaller 47 mg dose, the effect is proportionally smaller, but to err on the side of caution, finishing the last cup 5–6 hours before bed is sensible. With a 23:00 bedtime, that means no later than 17:00–18:00. Our latest cup before bedtime tool computes the exact cutoff for your schedule. People who know they are slow caffeine metabolisers — about half the population carries CYP1A2 variants that double caffeine half-life — may need to set an even earlier last-call time and can model this by adjusting the half-life in the calculator.

Adolescents are another group to watch. The EFSA suggests 3 mg per kg of body weight as a safe daily limit for children and teens, meaning a 40 kg teenager could have up to 120 mg from all sources, or about 2.5 cups of black tea. For smaller children, even one cup can be near the threshold. For body-weight-based calculations, use our safe daily limit by body weight tool.

Among teas, black tea’s 47 mg per cup places it in a comfortable middle range. It is nearly identical to Earl Grey tea (47 mg) and only 3 mg short of English Breakfast tea (50 mg). It delivers significantly more caffeine than green tea (28 mg), white tea (16 mg), and oolong tea (37 mg). At the same time, it is far outclassed by matcha (70 mg) and yerba mate (85 mg).

Compared with coffee, black tea is unmistakably milder. A matching 240 ml cup of drip coffee provides 96 mg — double the caffeine. A single 30 ml shot of espresso packs 63 mg, meaning black tea has 25% less caffeine than even a small espresso. If concentration matters, black tea’s 19.6 mg per 100 ml is far below espresso’s 210 mg per 100 ml, making it a gentle sipping option.

What changes the number for Black tea

The 47 mg figure is a population midpoint for a standard 240 ml cup of black tea prepared with near-boiling water and a 3–4 minute steep. Real-world cups vary widely. The single most influential factor is steeping time: a 1-minute dunk may extract as little as 20 mg, while a robust 5-minute brew can yield 60–70 mg, according to USDA reports and cross-validation by analytical labs. Water temperature is the next strong lever — using water at 100°C nearly doubles the caffeine extraction rate compared to 80°C. Leaf particle size also matters; tea bag grades (broken leaves) expose more surface area and release caffeine faster than whole-leaf orthodox grades.

Beyond the basics, even the material of the tea bag and the mineral content of the water can nudge the final cup. Paper bags may absorb some caffeine-containing oils, while mesh or pyramid bags allow greater flow. Hard water, with its dissolved minerals, can alter extraction kinetics slightly, though the effect is usually under 5%. Therefore, the same tea leaves in different kitchens can produce measurable differences.

Decaffeinated black tea still delivers a trace: typically 2–5 mg per 240 ml cup. If you switch to a larger mug, say 350 ml (12 fl oz), expect a proportional rise — approximately 70 mg. For ready-to-drink bottled black teas, the numbers often dip because of higher dilution and milder brewing; for example, a 355 ml bottle of generic iced tea averages 45 mg total, equivalent to about 30 mg per 240 ml. Our central 47 mg value is therefore best seen as the most likely result under standard home and café conditions, with a practical range of 40–60 mg.

• Steeping time: 1 min → ~20 mg; 3–4 min → 47 mg; 5 min → ~65 mg
• Water temperature: 80°C → slower extraction; 100°C → faster extraction
• Leaf form: tea bag (broken) → faster release; loose whole leaf → slightly slower
• Serving size: 240 ml → 47 mg; 350 ml mug → ~70 mg
• Decaf black tea: 2–5 mg per 240 ml

Where this figure comes from

The 47 mg figure is sourced from the USDA FoodData Central (FDC ID 143227, “Beverages, tea, black, brewed, prepared with tap water”), which reports a mean of 47 mg per 8 fl oz (237 ml). This value is corroborated by the Mayo Clinic caffeine chart (40–50 mg range) and the EFSA 2015 caffeine safety assessment.

Published figures for black tea caffeine differ because of real variation in tea products and brewing. Some lab analyses measure as low as 25 mg and as high as 78 mg per cup, depending on tea origin (Assam tends higher, Darjeeling lower), leaf grade, and preparation. Our editorial methodology is to adopt the USDA’s most representative value and to update it when new, rigorously sampled data emerge. You can examine the full open-source dataset and its documentation at our open caffeine dataset. If you have a credible source suggesting a revision, we welcome submissions.

Bottom line

A 240 ml cup of black tea contains 47 mg of caffeine — roughly half the caffeine of a same-sized drip coffee (96 mg) and about 12% of the FDA’s 400 mg daily maximum. This moderate dose delivers a smooth, gradual alertness that typically lasts three to five hours, with a half-life of 5.7 hours leaving 23 mg after 6 hours and 11 mg after 12 hours. For most healthy adults, drinking a few cups throughout the day fits safely within guidelines, provided the last cup is consumed by early evening to protect sleep. For those monitoring intake, our tools can help tailor the timing to your body and schedule.